The film, which opened March 21, continued the Muppet tradition of great celebrity cameos. Who could forget Steve Martin as a surly waiter in 1979's The Muppet Movie?

"It's the blink-and-you'll-miss-it ones that are really fun," says writer-director James Bobin.

Some of appearances, such as getting Usher to play a wedding usher, are written into the script, says Bobin, while others just seem to happen spontaneously. For example, Bobin knew he needed Sean Combs for a Muppets celebration scene.